Compounds and methods for preparation of diarylpropanes

ABSTRACT

Compounds of structure (I): 
                         
including stereoisomers, tautomers and salts thereof, wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , X, Y and Z are as defined herein. Such compounds are useful for the preparation of diarylpropane compounds. Methods for the preparation of compounds of structure (I) are also disclosed, as are methods employing compounds of structure (I) for the preparation of diarylpropanes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 13/425,959, filed Mar. 21, 2012, now allowed, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/467,286 filed Mar. 24, 2011, which applications are incorporated herein by reference in their entirety.

BACKGROUND

1. Technical Field

The present invention is generally directed to compounds useful for the preparation of diarylpropanes and methods related to the same.

2. Description of the Related Art

There is great demand for products able to inhibit or prevent excessive pigmentation of the skin. Melanin, the skin's natural pigment, is a nitrogenous polymer synthesized in melanosomes, which are membrane-bound organelle present within melanocytes. Melanin is produced in varying concentrations, depending on skin type (genetic disposition) and environmental conditions. Melanocytes are cells that occur in the basal membrane of the epidermis, and account for between 5% and 10% of the cellular content (approximately 1200-1500 melanocytes/cm²). When stimulated, by factors such as ultraviolet (UV) light, melanocytes divide more rapidly and produce greater quantities of melanin. The melanin is then transported in mature melanosomes to keratinocytes within the epidermis where it becomes visible as a brown skin color.

The over production of melanin can cause different types of abnormal skin color, hair color and other diseases and conditions of the skin. There are primarily two conditions related to skin pigmentation disorders. A darkening of the skin that includes abnormal elevated melanin caused by UV exposure and aging; and abnormal distribution of skin pigments resulting in age spots, liver spots, and drug and wound/disease induced hyperpigmentation (Seiberg et al. (2000) J. Invest. Dermatol. 115:162; Paine et al. (2001) J. Invest. Dermatol. 116:587).

Diarylalkanes are a rare class of natural product which have shown potential for decreasing melanin production and are being investigated for use as skin lightening therapeutics (see e.g., U.S. Pub. No. 2005/0267047). Although more than 179,000 natural compounds are listed in the Dictionary of Natural Products (Chapman & Hall/CRC, Version 12:2 Jan. 2004, available on CD-ROM), only 82 are diarylpropanes. Diarylpropanes have been isolated from a number of different natural sources; however, the low abundance of diarylpropanes of interest in natural sources often necessitates their preparation in the laboratory.

One approach for preparing diarylpropanes has been to completely reduce the corresponding chalcone to the diarylpropane in one step (see e.g., U.S. Pat. No. 5,880,314; J. Chem. Soc. Perkin Trans. 1 (1979), (7), 1661-4; and Lett. In Org. Chem. 2006, 3, 39-41. However, such methods are not robust and are unsuitable for large-scale preparation of diarylpropanes. For example, published methods generally suffer from low yields, poor reproducibility and result in mixtures of compounds which are difficult to separate. Methods and/or compounds to successfully address these, and other, difficulties associated with preparation of diarylpropanes have yet to be suggested.

While significant advances have been made in this field, there remains a need for improved methods for preparation of diarylpropanes as well as compounds useful for the same. In particular, methods and compounds suitable for large-scale preparation of diarylpropanes in high purity are needed. The present invention fulfills these needs, and provides other related advantages.

BRIEF SUMMARY

In brief, this invention is generally directed to compounds having the following structure (I):

or a stereoisomer, tautomer or salt thereof, wherein R¹, R², R³, R⁴, R⁵, R⁶, X, Y and Z are as defined below.

Compounds of structure (I) above have utility over a wide range of applications. For example, the disclosed compounds may be used in methods for the preparation of diarylpropane compounds. Such methods result in better purity and higher yield of diarylpropane than other known methods. Accordingly, in one embodiment the present disclosure is directed to a method for preparation of diarylpropanes having the following structure (II):

or a stereoisomer, tautomer or salt thereof, wherein R⁷, R⁸, R⁹ and R¹⁰ are as defined below. The method for preparation of compounds of structure (II) comprises reduction of compounds of structure (I). The robust character of the disclosed methods makes the methods more amenable to large-scale production of diarylpropanes compared to previous methods.

These and other aspects of the invention will be apparent upon reference to the following detailed description. To this end, various references are set forth herein which describe in more detail certain background information, procedures, compounds and/or compositions, and are each hereby incorporated by reference in their entirety.

DETAILED DESCRIPTION

As mentioned above, this invention is generally directed to compounds useful for the preparation of diarylpropanes, as well as to methods related to the same. In one embodiment, compounds are disclosed which have the following structure (I):

or a stereoisomer, tautomer or salt thereof, wherein:

R¹, R², R³ and R⁴ are each independently hydrogen, alkyl, aryl or aralkyl;

one of R⁵ or R⁶ is oxo, and the other of R⁵ or R⁶ is hydrogen; and

X, Y and Z are each independently absent or hydrogen, or X and Y or Z and Y may join to form a bond, wherein X, Y and Z are each chosen such that all valences are satisfied.

As used herein, the following terms have the meanings set forth below.

“Alkyl” means an optionally substituted, straight chain or branched, noncyclic or cyclic, unsaturated or saturated aliphatic hydrocarbon containing from 1 to 10 carbon atoms. Representative saturated straight chain alkyls include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, and the like; while saturated branched alkyls include isopropyl, sec-butyl, isobutyl, tert-butyl, isopentyl, and the like. Representative saturated cyclic alkyls include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and the like; while unsaturated cyclic alkyls include cyclopentenyl and cyclohexenyl, and the like. Cyclic alkyls are also referred to herein as “homocycles” or “homocyclic rings.” Unsaturated alkyls contain at least one double or triple bond between adjacent carbon atoms (referred to as an “alkenyl” or “alkynyl”, respectively). Representative straight chain and branched alkenyls include ethylenyl, propylenyl, 1-butenyl, 2-butenyl, isobutylenyl, 1-pentenyl, 2-pentenyl, 3-methyl-1-butenyl, 2-methyl-2-butenyl, 2,3-dimethyl-2-butenyl, and the like; while representative straight chain and branched alkynyls include acetylenyl, propynyl, 1-butynyl, 2-butynyl, 1-pentynyl, 2-pentynyl, 3-methyl-1-butynyl, and the like.

“Allyl” means an alkyl group, as defined above, comprising a methylene connected to a terminal alkene, for example —CH₂CH═CH₂.

“Alkoxy” means an alkyl moiety as defined above (i.e., an optionally substituted, straight chain or branched, noncyclic or cyclic, unsaturated or saturated aliphatic hydrocarbon containing from 1 to 10 carbon atoms) attached through an oxygen bridge (i.e., —O-alkyl) such as methoxy, ethoxy, and the like.

“Aryl” means an optionally substituted aromatic carbocyclic moiety such as phenyl, naphthyl and the like.

“Aralkyl” means one or more aryl moieties as defined above attached through an alkyl bridge (i.e., -alkyl-(aryl)_(n), wherein n is 1, 2 or 3). Non-limiting examples of aralkyl moieties include benzyl (—CH₂-phenyl, i.e., Bn), diphenyl methyl (—CH₂-(phenyl)₂) and trityl (—C-(phenyl)₃).

“Heterocycle” (also referred to herein as a “heterocycle ring”) means an optionally substituted 5- to 7-membered monocyclic, or an optionally substituted 7- to 14-membered polycyclic, heterocycle ring which is either saturated, unsaturated or aromatic, and which contains from 1 to 4 heteroatoms independently selected from nitrogen, oxygen and sulfur, and wherein the nitrogen and sulfur heteroatoms may be optionally oxidized, and the nitrogen heteroatom may be optionally quaternized, including bicyclic rings in which any of the above heterocycles are fused to a benzene ring as well as tricyclic (and higher) heterocyclic rings. The heterocycle may be attached via any heteroatom or carbon atom. Heterocycles include “heteroaryl” which is an optionally substituted aromatic heterocycle ring of 5- to 10-members and having at least one heteroatom selected from nitrogen, oxygen and sulfur, and containing at least 1 carbon atom, including both mono- and bicyclic ring systems. Representative heteroaryls include (but are not limited to) furyl, benzofuranyl, thiophenyl, benzothiophenyl, pyrrolyl, indolyl, isoindolyl, azaindolyl, pyridyl, quinolinyl, isoquinolinyl, oxazolyl, isooxazolyl, benzoxazolyl, pyrazolyl, imidazolyl, benzimidazolyl, thiazolyl, benzothiazolyl, isothiazolyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, cinnolinyl, phthalazinyl, and quinazolinyl. Thus, in addition to the aromatic heteroaryls listed above, heterocycles also include (but are not limited to) morpholinyl, pyrrolidinonyl, pyrrolidinyl, piperizinyl, piperidinyl, hydantoinyl, valerolactamyl, oxiranyl, oxetanyl, tetrahydrofuranyl, tetrahydropyranyl, tetrahydropyridinyl, tetrahydroprimidinyl, tetrahydrothiophenyl, tetrahydrothiopyranyl, tetrahyd ropyrim id inyl, tetrahydrothiophenyl, tetrahydrothiopyranyl, and the like.

An “optionally substituted” alkyl, aryl or aralkyl means an alkyl, aryl, or aralkyl moiety as defined above, wherein 0 to 4 hydrogen atoms of the aliphatic hydrocarbon or heterocycle are replaced with a substituent. When zero hydrogen atoms are replaced with a substituent, the alkyl, aryl, or aralkyl moiety is unsubstituted. When 1 to 4 hydrogen atoms are replaced with a substituent, the alkyl, aryl, or aralkyl moiety is substituted. In the case of an oxo substituent (“═O”) two hydrogen atoms from the same carbon atom are replaced. When substituted, “substituents” within the context of this invention include oxo, halogen, hydroxyl, alkoxy or —NR^(a)R^(b), wherein R^(a) and R^(b) are the same or different and independently hydrogen or alkyl moiety as defined above, or R^(a) and R^(b) are taken together with the nitrogen to which they are attached to form a heterocycle as defined above.

“Oxo” means ═O (i.e., carbonyl).

“Hydroxyl” means —OH.

“Halogen” means fluoro, chloro, bromo and iodo.

In more specific embodiments of the compound of structure (I), R⁵ is oxo, R⁶ is hydrogen and the compound of structure (I) has one of the following structures (IA) or (IB):

In other embodiments, each of R¹ and R² are alkyl. For example, in some aspects each of R¹ and R² are methyl and the compound of structure (I) has one of the following structures (IA-1) or (IB-1):

In some other embodiments, each of R³ and R⁴ are aralkyl. For example, in some embodiments, each of R³ and R⁴ are benzyl and the compound of structure (I) has one of the following structures (IA-2) or (IB-2):

In yet other embodiments, each of R³ and R⁴ are alkyl. For example, in some aspects each of R³ and R⁴ are isopropyl and the compound of structure (I) has one of the following structures (IA-3) or (IB-3):

In other embodiments, each of R³ and R⁴ are hydrogen and the compound of structure (I) has one of the following structures (IA-4) or (IB-4):

In certain other embodiments, R⁶ is oxo, R⁵ is hydrogen and the compound of structure (I) has one of the following structures (IC) or (ID):

In some other embodiments, each of R¹ and R² are alkyl. For example, in some aspects each of R¹ and R² are methyl and the compound of structure (I) has one of the following structures (IC-1) or (ID-1):

In yet other embodiments, each of R³ and R⁴ are aralkyl. For example, in some embodiments, R³ and R⁴ are benzyl and the compound of structure (I) has one of the following structures (IC-2) or (ID-2):

In some other embodiments, each of R³ and R⁴ are alkyl. For example, in some aspects each of R³ and R⁴ are isopropyl and the compound of structure (I) has one of the following structures (IC-3) or (ID-3):

In some other embodiments, each of R³ and R⁴ are hydrogen and the compound of structure (I) has one of the following structures (IC-4) or (ID-4):

In some other embodiments, at least one of R³ or R⁴ is allyl. For example, in some embodiments, each of R³ and R⁴ are allyl.

In some embodiments, at least one of R³ or R⁴ is alkyl. In certain other embodiments, at least one of R¹ or R² is methyl. For example, in some embodiments each of R¹ and R² is methyl.

In other embodiments, at least one of R³ or R⁴ is aralkyl.

In other embodiments, the compound of structure (I) has one of the following structures (IA-5), (IA-6), (IA-7) or (IA-8):

In still other embodiments, the compound of Structure (I) has one of the following structures (IB-5), (IB-6), (IB-7) or (IB-8):

In yet other embodiments, the compound of structure (I) has one of the following structures (IC-5), (IC-6), (IC-7) or (IC-8):

In still other embodiments, the compound of structure (I) has one of the following structures (ID-5), (ID-6), (ID-7) or (ID-8):

In yet other embodiments, at least one of R³ or R⁴ is allyl. For example, in some aspects each of R³ and R⁴ are allyl. In yet other embodiments, at least one of R³ or R⁴ is benzyl.

The present disclosure is also directed to a method for preparing a compound of structure (II):

or a stereoisomer, tautomer or salt thereof, wherein:

R⁷, R⁸, R⁹ and R¹⁰ are each independently hydrogen, alkyl, aryl or aralkyl,

the method comprising reducing a compound of structure (I):

or a stereoisomer, tautomer or salt thereof, wherein:

R¹, R², R³ and R⁴ are each independently hydrogen, alkyl, aryl or aralkyl;

one of R⁵ or R⁶ is oxo, and the other of R⁵ or R⁶ is hydrogen; and

X, Y and Z are each independently absent or hydrogen, or X and Y or Z and Y may join to form a bond, wherein X, Y and Z are each chosen such that all valences are satisfied.

In some embodiments of the disclosed method, the compound of structure (I) has one of the following structures (IB) or (ID):

In other embodiments of the disclosed method, each of R¹ and R² are methyl. In certain other embodiments, each of R³ and R⁴ are hydrogen. For example, in some aspects each of R¹ and R² are methyl, each of R³ and R⁴ are hydrogen and the compound of structure (I) has one of the following structures (IB-7) or (ID-7):

In some embodiments of the disclosed method, reducing comprises treating a compound of structure (IB) or (ID) with sodium bis(2-methoxyethoxy)aluminum hydride, Raney nickel and hydrogen gas or zinc/HCl.

In certain other embodiments of the disclosed method, the compound of structure (IB) or (ID) has been prepared by reducing a compound of structure (IA) or (IC), respectively:

For example, in some embodiments of the foregoing method, each of R¹ and R² are methyl, each of R³ and R⁴ are benzyl or each of R³ and R⁴ are isopropyl. For example, in some aspects, each of R¹ and R² are methyl, each of R³ and R⁴ are benzyl and the compound of structure (I) has one of the following structures (IA-5) or (IC-5):

In certain examples of the foregoing method, each of R¹ and R² are methyl, each of R³ and R⁴ are isopropyl and the compound of structure (I) has one of the following structures (IA-6) or (IC-6):

In yet other embodiments, reducing comprises treating a compound of structure (IA) or (IC) with palladium on carbon and formic acid/H₂ (gas) or palladium on carbon and ammonium formate.

In certain other embodiments of the disclosed method, the compound of structure (I) has been prepared by reaction of a compound of structure (III) and a compound of structure (IV):

or a stereoisomer, tautomer or salt thereof, wherein one of R¹¹ or R¹² is hydrogen and the other of R¹¹ or R¹² is methyl. For example, in some embodiments, R¹¹ is hydrogen and R¹² is methyl. In some other exemplary embodiments, R¹¹ is methyl and R¹² is hydrogen. In some embodiments, each of R¹ and R² are methyl, each of R³ and R⁴ are benzyl or each of R³ and R⁴ are isopropyl.

In yet other embodiments of the disclosed method, the compound of structure (I) has one of the following structures (IB) or (ID):

For example, in some embodiments of the foregoing method, each of R¹ and R² are methyl, each of R³ and R⁴ are benzyl or each of R³ and R⁴ are isopropyl. In certain other embodiments, each of R¹ and R² are methyl, each of R³ and R⁴ are benzyl and the compound of structure (I) has one of the following structures (IA-5) or (IC-5):

In some embodiments of the foregoing method, reducing comprises the steps of:

-   -   (a) treatment with palladium on carbon and formic acid/H₂ (gas)         or palladium on carbon and ammonium formate; and     -   (b) treatment with sodium bis(2-methoxyethoxy)aluminum hydride,         Raney nickel and hydrogen gas or zinc/HCl.

In yet other embodiments of the disclosed method, each of R¹ and R² are methyl, each of R³ and R⁴ are isopropyl and the compound of structure (I) has one of the following structures (IA-6) or (IC-6):

In some embodiments of the foregoing method, reducing comprises treating a compound of structure (IA-6) or (IC-6) with palladium on carbon, hydrogen gas and acetic acid.

In yet other embodiments, the compound of structure (II) has the following structure (II-2):

In still other embodiments, the compound of structure (II) has the following structure (II-1):

1. Preparation of 1,3-Diarylpropanes

A. Comparative Preparations of 1,3-diarlypropanes

Various reports have described the preparation of 1,3-diarylpropanes; however, none of the reported methods meet the criteria required for safe and cost-effective preparation of these compounds at large scales. For example, U.S. Pat. No. 5,880,314 describes the preparation of 1,3-bis(2,4-dihydroxyphenyl)propane by complete reduction of the corresponding chalcone. A small quantity (˜6 grams) of the chalcone was treated with Raney nickel and hydrogen gas for an extended period of time (˜20 hours), and an approximately 23% yield of purified 1,3-diarylpropane was obtained. Although preparation of 1,3-diarylpropanes was feasible via this method, the low yield and use of explosive mixtures of hydrogen gas and Raney nickel make this method unsuitable for large-scale production.

A one step reduction of Chalcones to 1,3-diarylpropanes has also been reported in J Braz. Chem. Soc, 1999, 10, 347-353. However, the disclosed method is not suitable for preparation of compounds of structure (II) because it results in a mixture of compounds which are difficult to separate. In addition, the disclosed methods suffer from a lack of reproducibility from batch to batch.

A one step reduction of chalcones to saturated alcohols with ammonium formate/Pd-Carbon has also been reported (Lett. In Org. Chem. 2006, 3, 39-41). However, this method does not include complete reduction to a 1,3-diarylpropane and does not address the deficiencies of other preparation methods.

B. Improved Preparation of 1,3-Diarylpropanes

As noted above, known compounds and methods are unsuitable for preparation of compounds of structure (II), particularly at large scales. The compounds and methods provided by the present disclosure address the problems previously associated with preparation of 1,3-diarylpropane compounds. Reduction of a novel chalcone compound (i.e., a compound of structure (I)) to the corresponding ketone, followed by complete reduction of the ketone, results in 1,3-diarylpropanes in high yield and purity. In addition, the compounds and methods of the present disclosure allow for safer operation and easier reagent handling than when other known compounds and methods are employed. Accordingly, this new approach is amenable to safe and cost-effective production of 1,3-diarylpropanes at scales not obtainable (e.g., pilot plant or larger) when compounds of structure (I) are not used.

Methods of the present disclosure include preparation of compounds of structure (II) via a two-step reduction of compounds of structure (I). In certain embodiments, the methods result in at least a 25% increased yield of 1,3-diarylpropane relative to other known methods. Accordingly, in some embodiments complete reduction of a compound of structure (I) yields at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or at least 99% of the theoretical maximum of a compound of structure (II).

In addition to increased yield, the methods of the invention also provide for 1,3-diarylpropane compounds of higher purity than possible when other methods are employed. This high purity makes compounds of structure (II), prepared according to the present disclosure, easier to crystallize, thus increasing their purity even higher. Accordingly, in some embodiments compounds of structure (II) prepared according to the disclosed method have a purity of at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.5%, at least 99.9% or at least 99.99% as determined by HPLC.

The compounds of the present invention may be prepared by known organic synthesis techniques, including the methods described in more detail in the Examples. However in general, the compounds of structure (I) and (II) may be made by the following General Reaction Scheme (Scheme 1), wherein L is an appropriate leaving group (e.g., halogen), and the values for R¹-R¹², X, Y and Z are as defined above.

Referring to Scheme 1, compounds of structure (IIIA) can be purchased or prepared according to methods known in the art. Reaction of the phenolic hydroxyls with R³L under basic conditions (e.g., potassium or sodium carbonate) followed by reaction with R⁴L under basic conditions yields compounds of structure (III). In one specific example, R³ and R⁴ are each benzyl and R³L and R⁴L are each benzyl chloride. In another specific example, R³ and R⁴ are each isopropyl and R³L and R⁴L are each 2-bromopropane. One skilled in the art will recognize that when R³═R⁴, both groups can be added in a single step. In addition, the order of reaction may be reversed, and or appropriate protecting groups employed to obtain the desired compound of structure (III).

In a similar manner, compounds of structure (IVA) can be reacted with R¹L followed by R²L under basic conditions to yield compounds of structure (IV). In one specific example, R¹ and R² are each methyl and R¹L and R²L are each an appropriate methylating reagent (e.g., methyl iodide, etc.). Again, in certain embodiments wherein R¹═R² only one step may be required and variations to the order of reaction and protecting group schemes are possible.

Aldol condensation of compounds of structure (III) with compounds of structure (IV) under basic conditions then yields compounds of structure (I). In this context, various conditions may be employed in practicing the disclosed method. For example, reagents such as NaH, KOH, NaOH, LiOH, NaOMe, t-BuOK and the like may be employed to perform the aldol condensation. In certain embodiments, KOH in a solvent such as methanol may be used.

Compounds of structure (I) wherein R⁵ is oxo and Y and Z form a bond can be reduced to form compounds of structure (IB). Appropriate reduction conditions include conditions known in the art for reduction of the alkene bond in alpha-beta unsaturated carbonyl compounds. Such conditions include, but are not limited to, hydrogenation in the presence of an appropriate catalyst (e.g., palladium on carbon) and a hydrogen source such as hydrogen gas, formic acid, ammonium formate, cyclohexa-1,4-diene and other reagents capable of donating a hydrogen atom. In certain embodiments, transfer hydrogenation conditions (e.g., a catalyst and a hydrogen atom donor such as ammonium formate or formic acid) are particularly useful as such conditions can be safer, and in certain examples the reagents may be easier to handle than hydrogen gas, especially at large scales. In one specific example, the reduction conditions comprise a palladium catalyst (e.g., Pd/C) and ammonium formate. In other examples, the reaction conditions comprise a palladium catalyst (e.g., Pd/C) and formic acid and/or hydrogen gas. Other exemplary reagents for transfer hydrogenation include (Ph₃P)RhCl-EtSiH-Bz, NaBH₄-pyridine, NaBH₄—NiCl₂-Dioxane-MeOH (see e.g., J. Chem. Res. 2006, 584-585). Alternatively, compounds of structure (ID) can be prepared under similar conditions by reduction of compounds of structure (I) wherein R⁶ is oxo and X and Y form a bond.

Compounds of structure (II) can be prepared by complete reduction of the carbonyl group of compounds of structure (IB) or (ID) under appropriate conditions. Reduction conditions in this context include, but are not limited to, hydrogenation in the presence of an appropriate catalyst (e.g., Pd/C, Raney nickel and the like) and hydrogen gas. Other reduction conditions include treatment with zinc/HCl or Vitride® (i.e., sodium bis(2-methoxyethoxy)aluminum hydride) or other hydride reagents. In one specific example, the reduction conditions comprise treatment with Vitride®. In another example, reduction comprises treatment with Raney Ni/H₂ and Zn/HCl. Other reduction conditions are well known to those skilled in the art.

Alternatively, compounds of structure (II) can be prepared in a one-step reduction of compounds of structure (I). Appropriate conditions in this context include treatment of compounds of structure (I) with an appropriate catalyst (e.g., palladium on carbon) and hydrogen gas. In some embodiments, an acid, such as acetic acid may also be used in addition to a catalyst and hydrogen gas. In other embodiments, transfer hydrogenation conditions may be employed. In some examples of a one-step reduction of compounds of structure (I) to compounds of structure (II), at least one of R³ or R⁴ is isopropyl. For example, each of R³ and R⁴ may be isopropyl.

One skilled in the art will recognize that variations to the exact steps and reagents outlined in Scheme 1 are possible. In addition, protecting groups may be utilized in the preparation of the disclosed compounds. For example, in certain embodiments, the values of R¹, R², R³ or R⁴ are chosen such that a protected hydroxyl group results. In particular embodiments, R³ and R⁴ are hydroxyl protecting groups that can be removed to reveal a free phenol. Protecting groups useful in this context include protecting groups that can be removed by hydrogenation or under acidic, basic or other selective conditions. For example, alkyl (e.g., isopropyl, allyl and the like), aryl, aralkyl (e.g., benzyl, trityl and the like), are all useful hydroxyl protecting groups which may be employed in the context of the current disclosure.

In one particular embodiment, one or both of R³ and R⁴ are protecting groups which can be removed by hydrogenation, for example, benzyl groups. In other embodiments, one or both of R³ and R⁴ are isopropyl. Isopropyl can be selectively removed by treatment with AlCl₃ or other Lewis acids (J. Org. Chem. 1998, 64, 9139). Advantages of using isopropyl as a protecting group within the context of the present disclosure include: 1) low molecular weight compared to other protecting groups so there is less mass loss; when the protecting group is removed 2) the isopropyl compound is soluble in methanol; 3) one step reduction to 1,3-diarylpropane is possible so expensive vitride reduction step can be avoided; and 4) selective deprotection of the isopropyl group proceeds in high yield. The protecting groups can be removed during one of the above described reaction steps (e.g., benzyl groups may be removed during the hydrogenation of the alkene bond) or additional steps may added to the above scheme to remove the protecting groups. Such additional steps may include treatment with AlCl₃ or other appropriate reagent. Other protecting groups useful within the context of the present disclosure are well known to those of skill in the art, for example, those found in “Greene's Protective Groups in Organic Synthesis”, 4th Edition, Peter G. M. Wuts and Theodora W. Greene, October 2006 which is hereby incorporated by reference in its entirety.

Compounds of the present disclosure can be purified using known purification techniques. Such techniques include, but are not limited to, chromatography (e.g., HPLC, column chromatography, TLC, etc.), trituration, extraction, salt formation, crystallization, etc. In certain embodiments, crystallization techniques are employed for purification of compounds of structure (I) or (II). Such techniques are especially useful at large scale where other purification techniques are not feasible.

The compounds of the present invention may generally be utilized as the free acid (e.g., phenol) or free base. Alternatively, the compounds of this invention may be used in the form of acid or base addition salts. Acid addition salts of amino compounds of the present invention may be prepared by methods well known in the art, and may be formed from organic and inorganic acids. Suitable organic acids include maleic, fumaric, benzoic, ascorbic, succinic, methanesulfonic, acetic, trifluoroacetic, oxalic, propionic, tartaric, salicylic, citric, gluconic, lactic, mandelic, cinnamic, aspartic, stearic, palmitic, glycolic, glutamic, and benzenesulfonic acids. Suitable inorganic acids include hydrochloric, hydrobromic, sulfuric, phosphoric, and nitric acids. Base addition salts include those salts that form with a phenol or enol anion or with other acidic moieties and include salts formed with organic and inorganic cations such as those chosen from the alkali and alkaline earth metals (for example, lithium, sodium, potassium, magnesium, barium and calcium), as well as the ammonium ion and substituted derivatives thereof (for example, dibenzylammonium, benzylammonium, 2-hydroxyethylammonium, and the like). Thus, the term “salt” of structure (I) or structure (II) is intended to encompass any and all acceptable salt forms.

With regard to stereoisomers, the compounds of structure (I) or (II) may have chiral centers and may occur as racemates, enantiomerically enriched mixtures and as individual enantiomers or diastereomers. For ease of representation, the compounds of structure (I) are depicted in a trans configuration; however, the compounds of structure (I) may exist as E or Z isomers (i.e., cis or trans). All such isomeric forms are included within the present invention, including mixtures thereof. Compounds of structure (I) or (II) may also possess axial chirality which may result in atropisomers. Furthermore, some of the crystalline forms of the compounds of structure (I) or (II) may exist as polymorphs, which are included in the present invention. In addition, some of the compounds of structure (I) or (II) may also form solvates with water or other organic solvents. Such solvates are similarly included within the scope of this invention.

The compounds of the present disclosure may also exist in different tautomeric forms or as mixtures of tautomers. Tautomers are compounds that result from the formal migration of a hydrogen atom accompanied by a switch of a single bond and adjacent double bond. For example, the enol and keto form of a compound are tautomers of each other. Tautomers within the context of the present disclosure include, but are not limited to, the following tautomeric pairs (IB) and (IB-T) and (ID) and (ID-T):

Representative compounds of this invention include (but are not limited to) the compounds listed in Table 1 below.

TABLE 1 Representative Compounds Cmp. # Structure Name (IA-5)

(E)-1-(2,4- bis(benzyloxy)phenyl)-3-(2,4- dimethoxy-3- methylphenyl)prop-2-en-1-one (IA-6)

(E)-1-(2,4- diisopropoxyphenyl)-3-(2,4- dimethoxy-3- methylphenyl)prop-2-en-1-one (IA-7)

(E)-1-(2,4-dihydroxyphenyl)-3- (2,4-dimethoxy-3- methylphenyl)prop-2-en-1-one (IA-8)

(E)-1-(2,4-bis(allyloxy)phenyl)- 3-(2,4-dimethoxy-3- methylphenyl)prop-2-en-1-one (IB-5)

1-(2,4-bis(benzyloxy)phenyl)- 3-(2,4-dimethoxy-3- methylphenyl)propan-1-one (IB-6)

1-(2,4-diisopropoxyphenyl)-3- (2,4-dimethoxy-3- methylphenyl)propan-1-one (IB-7)

1-(2,4-dihydroxyphenyl)-3- (2,4-dimethoxy-3- methylphenyl)propan-1-one (IB-8)

1-(2,4-bis(allyloxy)phenyl)-3- (2,4-dimethoxy-3- methylphenyl)propan-1-one (IC-5)

(E)-3-(2,4- bis(benzyloxy)phenyl)-1-(2,4- dimethoxy-3- methylphenyl)prop-2-en-1-one (IC-6)

(E)-3-(2,4- diisopropoxyphenyl)-1-(2,4- dimethoxy-3- methylphenyl)prop-2-en-1-one (IC-7)

(E)-3-(2,4-dihydroxyphenyl)-1- (2,4-dimethoxy-3- methylphenyl)prop-2-en-1-one (IC-8)

(E)-3-(2,4-bis(allyloxy)phenyl)- 1-(2,4-dimethoxy-3- methylphenyl)prop-2-en-1-one (ID-5)

3-(2,4-bis(benzyloxy)phenyl)- 1-(2,4-dimethoxy-3- methylphenyl)propan-1-one (ID-6)

3-(2,4-diisopropoxyphenyl)-1- (2,4-dimethoxy-3- methylphenyl)propan-1-one (ID-7)

3-(2,4-dihydroxyphenyl)-1- (2,4-dimethoxy-3- methylphenyl)propan-1-one (ID-8)

3-(2,4-bis(allyloxy)phenyl)-1- (2,4-dimethoxy-3- methylphenyl)propan-1-one (II-1)

4-(3-(2,4-dimethoxy-3- methylphenyl)propyl)benzene- 1,3-diol (II-2)

1-(3-(2,4- diisopropoxyphenyl)propyl)- 2,4-dimethoxy-3- methylbenzene

The following examples are provided for purposes of illustration, not limitation.

EXAMPLES

Certain compounds of the present disclosure may be prepared according to the following schemes and the knowledge of one skilled in the art. All temperatures are in degrees Celsius (° C.) unless otherwise indicated. All of the synthesized compounds were characterized by at least proton ¹H NMR, ¹³C NMR and LC/MS. During work up of reactions, the organic extract was dried over sodium sulfate (Na₂SO₄), unless mentioned otherwise. The following abbreviations are used for the commonly employed reagents: Na₂SO₄ (sodium sulfate), HCl (hydrochloric acid), NaOH (sodium hydroxide), KOH (potassium hydroxide), NaCl (sodium chloride), Pd—C (palladium on carbon), K₂CO₃ (potassium carbonate), NaHCO₃ (sodium bicarbonate), BnCl (Benzylchloride), DMF (Dimethyl Formamide) and RT (room temperature).

Example 1 Synthesis of 1-(2,4-bis(benzyloxy)phenyl)ethanone

To a mixture of 2,4-dihydroxyacetophenone 1 (1.00 equiv. 24 kg) and potassium carbonate (2.9 equiv. 63.3 kg) in dry DMF (235 L), benzylchloride (2.5 equiv., 50 kg) was added over 1 h at room temperature (25° C.). The reaction mixture was then heated at about 85-90° C. for ˜14 h and held at this temperature until found complete by HPLC. After completion, the reaction mixture was allowed to cool to room temperature (25° C.) and filtered through a bed of Celite®. The Celite® bed was washed with acetone (3 volumes), and the combined filtrate was concentrated in vacuo to a dry solid. This solid was dissolved in ethyl acetate (5 volumes) and washed with sodium bicarbonate solution (2×5 volumes) followed by brine (3 volumes). The ethyl acetate layer was then dried with sodium sulfate (75 kg), filtered and concentrated by evaporation to dryness. The residue was triturated with hexane (100 L) and filtered. This residue was then washed with hexane (35 L) and dried at 35-40° C. to a constant weight to obtain compound 2 (40 Kg) 77%. MP: 83.1° C.; ¹H-NMR (CDCl₃, 500 MHz): δ 7.86 (d, 1H, J=9 Hz), 7.55-7.41 (m, 8H), 7.40-7.36 (m, 2H), 6.65-6.63 (m, 1H), 6.62 (s, 1H), 5.13 (s, 2H), 5.10 (s, 2H), 2.57 (s, 3H); ¹³C-NMR (CDCl₃, 125 MHz): δ 197.762 (C), 169.511 (C), 160.106 (C), 136.190 (C), 136.019 (C), 132.729 (CH), 128.890 (CH), 128.724 (2CH), 128.568 (CH), 128.405 (CH), 128.298 (CH), 128.283 (CH), 127.635 (CH), 127.539 (CH), 121.779 (C), 106.325 (CH), 100.369 (CH), 70.753 (CH₂), 70.279 (CH₂), 32.145 (CH₃).

Example 2 Synthesis of (E)-1-(2,4-bis(benzyloxy)phenyl)-3-(2,4-dimethoxy-3-methylphenyl)prop-2-en-1-one

A solution of compound 2 (1.00 equiv., 40 kg) in MeOH (360 L) was cooled to 10-15° C. and treated with potassium hydroxide (5 equiv., 36 kg) in MeOH (360 L) over a period of 1.5 h. Next 2,4-dimethoxy-3-methylbenzaldehyde 3 (1.2 equiv., 25 kg) was added to the reaction mixture over 1.5 h while maintaining the temperature at 10-15° C. After the addition was complete, the reaction mixture was heated to 60-65° C. with stirring and held at this temperature until found complete by HPLC (˜20 h). After completion, the reaction mixture was cooled back down to 10-15° C. and quenched with 2N aqueous HCl (13.5 L) to pH 2. The solid formed at this stage was filtered, washed with water and dissolved in acetic acid (360 L). This mixture was then cooled to 22-25° C. and stirred for 20 min upon which a yellow crystalline solid formed. The solid was collected by filtration, washed with water and dried under vacuum to a constant weight at 30° C. to obtain (IA-5) (50 Kg, 84%. MP: 125.1° C.; ¹H-NMR (CDCl₃, 500 MHz): δ 7.93 (d, 1H, J=16 Hz), 7.83 (d, 1H, J=8.5 Hz), 7.54 (d, 1H, J=16 Hz), 7.46-7.43 (m, 5H), 7.42-7.40 (m, 1H), 7.39-7.37 (m, 1H), 7.32-7.30 (m, 3H), 7.15 (d, 1H, J=8.5 Hz), 6.69-6.67 (m, 2H), 6.53 (d, 1H, J=8.5 Hz), 5.13 (s, 2H), 5.12 (s, 2H), 3.87 (s, 3H), 3.69 (s, 3H), 2.15 (s, 3H); ¹³C-NMR (CDCl₃, 125 MHz): δ 190.599 (C), 162.977 (C), 160.380 (C), 159.365 (C), 159.080 (C), 137.633 (CH), 136.312 (C), 136.201 (C), 133.006 (CH), 128.246 (CH), 127.968 (CH), 127.576 (CH), 126.155 (CH), 125.970 (CH), 123.071 (C), 121.583 (C), 120.036 (C), 106.503 (CH), 100.706 (CH), 70.786 (CH₂), 70.290 (CH₂), 61.602 (CH₃), 55.691 (CH₃), 8.858 (CH₃).

Example 3 Synthesis of 1-(2,4-dihydroxyphenyl)-3-(2,4-dimethoxy-3-methylphenyl)propan-1-one

A solution of (IA-5) (1 equiv. 50 kg) in methanol (250 L) was treated with 10% Pd—C (10% by weight) and formic acid (250 L) and hydrogenated at 23-25° C. for 10 h. After the reaction was found complete by HPLC, the reaction mixture was filtered through Celite®. The Celite® bed was washed with ethyl acetate (40L), and the combined filtrate was concentrated under vacuum at 35-40° C. to dryness. The residue was dissolved in ethyl acetate (3 volumes), washed with saturated sodium bicarbonate solution (20 L) until a pH of 7-7.5 was obtained. The ethyl acetate layer was then further washed with water (150 L) followed by brine. The ethyl acetate layer was then dried with sodium sulfate (88 kg), filtered and concentrated under vacuum at 35-45° C. to a constant weight to yield the product (25 Kg, 78%). MP: 171.0° C.; ¹H-NMR (CDCl₃, 500 MHz): δ 12.79 (s, 1H), 7.69 (d, 1H, J=8.5 Hz), 7.02 (d, 1H, J=8.5 Hz), 6.61 (d, 1H, J=8.5 Hz), 6.38-6.34 (m, 2H), 5.63 (s, 1H), 3.82 (s, 3H), 3.76 (s, 3H), 3.20 (t, 2H, J=8 Hz), 2.99 (t, 2H, J=8 Hz), 2.18 (s, 3H); ¹³C-NMR (CDCl₃, 125 MHz): δ 204.899 (C), 165.218 (C), 162.323 (C), 157.592 (C), 157.359 (C), 132.425 (CH), 127.047 (CH), 125.688 (C), 119.917 (C), 113.910 (C), 107.561 (CH), 106.255 (CH), 103.508 (CH), 60.658 (CH₃), 55.657 (CH₃), 39.355 (CH₂), 25.423 (CH₂), 9.195 (CH₃).

Example 4 Synthesis of 4-(3-(2,4-dimethoxy-3-methylphenyl)propyl)benzene-1,3-diol

Under a nitrogen atmosphere, (IB-7) (1 equiv., 25 kg) was added into a reaction vessel containing THF (250 L) while stirring. The reaction mixture was then cooled to 0-5° C. and charged with Vitride® (i.e., sodium bis(2-methoxyethoxy)aluminum hydride, 1 equiv., 120 L) over 2.5 h. The reaction mixture was then heated and maintained at reflux until found complete by HPLC (˜16 h). Next, the reaction was cooled to 0-5° C., quenched with 150 L of concentrated HCl (30-36%) in water (150 L) and stirred for 30 min. The reaction mixture was then diluted with water (150 L) and extracted twice with ethyl acetate (450 L and 375 L). The combined ethyl acetate extract was washed with aqueous sodium bicarbonate (25 kg in 150 L of water) followed by saturated sodium chloride (150 L). Charcoal (3.25 Kg) was added to the organic layer and the mixture was refluxed for 20 minutes. This mixture was filtered through Celite® and washed with ethyl acetate (20 L). The ethyl acetate layer was then dried with anhydrous sodium sulfate (25 kg) and concentrated under vacuum at 40-45° C. The crude product thus obtained was triturated for 4 h with toluene (5 L) at room temperature and filtered. This residue was washed with toluene (16 L), and the solid thus obtained was dried under vacuum for 8 h at 55-60° C. to produce 16.9 Kg of crude product.

The crude product (16.9 Kg) from the previous stage was dissolved in acetone (4 L) with heating to 55° C. This solution was then cooled to room temperature (24° C.) and treated with water (60 L) while stirring. Stirring was continued for 10 h at room temperature before the resulting solids were allowed to settle to the bottom, and the top organic layer was carefully removed. The remaining mixture was then diluted with petroleum ether (13 L), stirred for an additional 5 h at room temperature, filtered and then dried under vacuum for 12 h at 60° C. Product from two such crystallizations was combined, dried, ground and sieved to obtain purified (II-1) (15.64 Kg, 93%). MP: 108.0° C.; ¹H-NMR (CDCl₃, 500 MHz): δ 6.96 (d, 1H, J=8.3 Hz), 6.85 (d, 1H, J=8.3 Hz), 6.62 (d, 1H, J=8.3 Hz), 6.27 (d, 1H, J=2.2 Hz), 6.21 (dd, 1H, J=2.2 Hz), 3.77 (s, 3H), 3.63 (s, 3H), 2.52-2.58 (m, 4H), 2.10 (s, 3H), 1.78-1.82 (m, 2H); ¹³C-NMR (CDCl₃, 125 MHz): δ 158.55 (C), 158.43 (C), 157.38 (C), 157.15 (C), 131.53 (CH), 128.95 (C), 128.28 (CH), 121.45 (C), 120.30 (C), 107.40 (CH), 103.60 (CH), 61.44 (CH₃), 56.19 (CH₃), 32.90 (CH₂), 30.77 (CH₂), 30.51 (CH₂), 9.195 (CH₃).

Example 5 Synthesis of 2,4-bis(benzyloxy)benzaldehyde

Using a procedure analogous to that described in Example 1, compound 4 is treated with benzyl chloride to obtain benzyl ether 5. Protecting groups are employed as needed.

Example 6 Synthesis of (E)-3-(2,4-bis(benzyloxy)phenyl)-1-(2,4-dimethoxy-3-methylphenyl)prop-2-en-1-one

In a manner analogous to that described in Example 2, compounds 5 and 6 are treated under basic conditions to yield chalcone (IC-5).

Example 7 Synthesis of 3-(2,4-dihydroxyphenyl)-1-(2,4-dimethoxy-3-methylphenyl)propan-1-one

In a manner similar to that described in Example 3, compound (IC-5) is reduced to yield (ID-7).

Example 8 Synthesis of 4-(3-(2,4-dimethoxy-3-methylphenyl)propyl)benzene-1,3-diol

Compound (II-1) is prepared and purified in a manner analogous to that described in Example 4.

Example 9 Synthesis of 1-(2,4-diisopropdxyphenyl)ethanone

To a mixture of 2,4-dihydroxyacetophenone 1 (60.8 g, 0.4 mol) and potassium carbonate (160 g, 1.16 mol) in dry acetone (400 ml), isopropyl bromide (123 g, 1 mol) was added over 1 h at room temperature (25° C.). The reaction mixture was then refluxed for 4 h and monitored by TLC. After completion, the reaction mixture was allowed to cool to room temperature (25° C.) and filtered through a bed of celite. The celite bed was washed with acetone (3×100 ml) and the combined filtrate was concentrated down to dry solid. This solid was dissolved in ethyl acetate (500 ml), and the ethyl acetate was washed sequentially with 5% HCl (200 ml), sodium bicarbonate (2×200 ml) and brine solution (200 ml). The ethyl acetate layer was then dried over sodium sulfate, filtered and concentrated by evaporation to dryness. The residue was triturated with hexane (500 ml) and filtered. The resulting residue was washed with hexane (2×200 ml) and then dried at 35˜40° C. to a constant weight to obtain compound 7 (90 g, 95% yield). ¹H-NMR (CDCl₃, 500 MHz): δ 7.81 (d, 1H, J=8.5 Hz), 6.48 (dd, 1H, J=2& 8.5 Hz), 6.41 (d, 1H, J=2.0 Hz), 4.66-4.59 (m, 2H), 2.59 (s, 3H), 1.42 (d, 6H, J=6.5 Hz), 1.36 (d, 6H, J=6.5 Hz).

Example 10 Synthesis of (E)-1-(2,4-diisopropdxyphenyl)-3-(2,4-dimethoxy-3-methylphenyl)prop-2-en-1-one

A solution of 2,4-diisopropoxyacetophenone 7 (47.2 g, 0.2 mol) in methanol (200 ml) was cooled to 10˜15° C. and treated with potassium hydroxide (56 g, 1 mol) in MeOH (200 ml) over a period of 1.5 h. 2,4-dimethoxy-3-methylbenzaldehyde (43.2 g, 0.24 mol) in MeOH (200 ml) was then added to the reaction mixture over 1.5 h at 10˜15° C. After the addition was complete, cooling was removed. The reaction mixture was then heated to 60˜65° C. with stirring for approximately 20 h and held at this temperature until determined to be complete by TLC. After completion, the reaction mixture was cooled to 10˜15° C. and quenched with 2 N aqueous HCl (150 ml) to pH 2. The solid formed at this stage was filtered, washed with water and dissolved in MeOH (500 ml). This methanol solution was then cooled to 22˜25° C. and stirred for 20 min by which time a yellow crystalline solid had formed. The solid was collected by filtration, washed with water and dried under vacuum to a constant weight at 30° C. to obtain (IA-6) (70 g, 88%). ¹H-NMR (CDCl₃, 500 MHz): δ 7.92 (d, 1H, J=16 Hz), 7.75 (d, 1H, J=9 Hz), 7.58 (d, 1H, J=16 Hz), 7.52 (d, 1H, J=9 Hz), 7.69 (d, 1H, J=9 Hz), 6.54 (dd, 1H, J=2 & 9 Hz), 6.46 (d, 1H, J=2 Hz), 4.64-4.59 (m, 2H), 3.87 (s, 3H), 3.66 (s, 3H), 2.17 (s, 3H) 1.38 (d, 16H, J=6 Hz).

Example 11 Synthesis of 1-(3-(2,4-diisopropdxyphenyl)propyl)-2,4-dimethoxy-3-methylbenzene

A solution of (IA-6) (60 g, 0.15 mol) in methanol (600 ml) was treated with 10% Pd—C (10% by weight) and acetic acid (60 ml) and hydrogenated under a hydrogen atmosphere at 23˜25° C. and 54 psi for 10 h. When the reaction was determined complete by TLC, the reaction mixture was filtered through celite, and the celite bed was washed with ethyl acetate (250 ml). The combined filtrate was then concentrated under vacuum at 35˜40° C. to dryness. The residue was dissolved in ethyl acetate (750 ml) and washed sequentially with saturated sodium bicarbonate solution (250 ml) to pH 7˜7.5, water (250 ml) and brine. The ethyl acetate layer was dried over sodium sulfate, filtered and then concentrated under vacuum at 35˜45° C. to constant weight to yield (II-2) (52 g, 90% yield). ¹H-NMR (CDCl₃, 500 MHz): 7.03 (d, 1H, J=8.5 Hz), 7.00 (d, 1H, J=8.5 Hz), 6.60 (d, 1H, J=8.5 Hz), 6.43 (d, 1H, J=2 Hz), 6.40 (dd, 1H, J=2 & 8.5 Hz), 4.52-4-48 (m, 2H), 3.82 (s, 3H), 3.72 (s, 3H), 2.64-2.59 (m, 4H), 2.17 (s, 3H), 1.33 (d, 6H, J=6 Hz), 1.32 (d, 6H, J=6 Hz); ¹³C-NMR (CDCl₃, 125 MHz): δ 157.304 (C), 156.996 (C), 156.830 (C), 156.582 (C), 130.004 (CH), 127.791 (C), 126.680 (CH), 124.267 (C), 119.466 (C), 106.151 (CH), 106.018 (CH), 102.512 (CH), 69.957 (CH), 69.731 (CH), 60.525 (CH₃), 55.631 (CH₃), 31.216 (CH₂), 29.794 (CH₂), 29.271 (CH₂), 22.202 (2, CH₃), 22.161 (2, CH₃), 9.147 (CH₃).

Example 12 Synthesis of 4-(3-(2,4-dimethoxy-3-methylphenyl)propyl)benzene-1,3-diol

A solution of (II-2) (38.6 g, 0.1 mol) in anhydrous CH₂Cl₂ (250 ml) was treated with AlCl₃ under an argon atmosphere at 0-5° C. The reaction mixture was then stirred for 3 h at room temperature until found complete by TLC. The reaction was then cooled to 0-5° C., quenched with saturated NH₄Cl, diluted with water (100 ml) and extracted with ethyl acetate (3×250 ml). The combined ethyl acetate extract was washed with aqueous sodium bicarbonate followed by brine (250 L). The ethyl acetate layer was then dried over dry sodium sulfate and concentrated under vacuum at 40˜45° C. The crude product thus obtained was dissolved in MeOH (500 ml) and refluxed for 20 minutes in charcoal (400 g). This suspension was filtered through celite and washed with ethyl acetate (25 L). The filtered solution was concentrated and crystallized in MeOH. The solid thus obtained was dried under vacuum for 8 h at 55-60° C. to produce (II-1) (24.2 g, 60% yield). MP: 108.0° C.; ¹H-NMR (CDCl₃, 500 MHz): δ 6.96 (d, 1H, J=8.3 Hz), 6.85 (d, 1H, J=8.3 Hz), 6.62 (d, 1H, J=8.3 Hz), 6.27 (d, 1H, J=2.2 Hz), 6.21 (dd, 1H, J=2.2 Hz), 3.77 (s, 3H), 3.63 (s, 3H), 2.52-2.58 (m, 4H), 2.10 (s, 3H), 1.78-1.82 (m, 2H); ¹³C-NMR (CDCl₃, 125 MHz): δ 158.55 (C), 158.43 (C), 157.38 (C), 157.15 (C), 131.53 (CH), 128.95 (C), 128.28 (CH), 121.45 (C), 120.30 (C), 107.40 (CH), 103.60 (CH), 61.44 (CH₃), 56.19 (CH₃), 32.90 (CH₂), 30.77 (CH₂), 30.51 (CH₂), 9.195 (CH₃).

Example 13 Synthesis of 2,4-diisopropdxybenzaldehyde

Compound 8 is prepared in a manner analogous to that described in Example 9. Protecting groups are employed as needed.

Example 14 Synthesis of (E)-3-(2,4-diisopropdxyphenyl)-1-(2,4-dimethoxy-3-methylphenyl)prop-2-en-1-one

Compound (IC-6) is prepared by aldol condensation of 8 and 3 in a manner analogous to that described in Example 10.

Example 15 Synthesis of 1-(3-(2,4-diisopropdxyphenyl)propyl)-2,4-dimethoxy-3-methylbenzene

Compound (II-2) is prepared from (IC-6) in a manner analogous to that described in Example 11.

All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety.

From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims. 

The invention claimed is:
 1. A compound having the following structure (I):

or a stereoisomer, tautomer or salt thereof, wherein: R¹ R² are each independently alkyl or aralkyl; R³ and R⁴ are each independently hydrogen, alkyl or aralkyl; one of R⁵ or R⁶ is oxo, and the other of R⁵ or R⁶ is hydrogen; and X, Y and Z are each independently absent or hydrogen, or X and Y or Z and Y may join to form a bond, wherein X, Y and Z are each chosen such that all valences are satisfied.
 2. The compound of claim 1, wherein R⁵ is oxo, R⁶ is hydrogen and the compound has the following structures (IA):


3. The compound of claim 2, wherein each of R¹ and R² are alkyl.
 4. The compound of claim 3, wherein each of R¹ and R² are methyl and the compound has the following structures (IA-1):


5. The compound of claim 2, wherein each of R³ and R⁴ are aralkyl.
 6. The compound of claim 5, wherein each of R³ and R⁴ are benzyl and the compound has the following structures (IA-2):


7. The compound of claim 2, wherein each of R³ and R⁴ are hydrogen and the compound has the following structures (IA-4):


8. The compound of claim 1, wherein R⁵ is oxo, R⁶ is hydrogen and the compound has the following structure (IA) (IB):


9. The compound of claim 8, wherein each of R¹ and R² are alkyl.
 10. The compound of claim 9, wherein each of R¹ and R² are methyl and the compound has the following structure (IB-1):


11. The compound of claim 10, wherein each of R³ and R⁴ are aralkyl.
 12. The compound of claim 11, wherein each of R³ and R⁴ are benzyl and the compound has the following structure (IB-2):


13. The compound of claim 2, wherein each of R³ and R⁴ are hydrogen and the compound has the following structure (IB-4):


14. A compound having the following structure:

or a salt or tautomer thereof.
 15. A compound having the following structure:

or a salt or tautomer thereof.
 16. A compound having the following structure:

or a salt or tautomer thereof.
 17. A method for preparing the following compound:

or a salt thereof, the method comprising reducing the compound of claim 14 in a first reducing step under first reducing conditions to form an intermediate product, and reducing the intermediate product in second reducing step under second reducing conditions.
 18. The method of claim 17, wherein the first reducing step comprises the following transformation:


19. The method of claim 17, wherein the second reducing step comprises the following transformation:


20. The method of claim 17, wherein the intermediate product has the following structure:


21. The method of claim 17, wherein the first reducing conditions comprise treatment with palladium on carbon and formic acid/H₂ (gas) or palladium on carbon and ammonium formate.
 22. The method of claim 17, wherein the second reducing conditions comprise treatment with sodium bis(2-methoxyethoxy)aluminum hydride, Raney nickel and hydrogen gas or zinc/HCl. 